A display apparatus using an organic electro luminescence (organic EL) device has been paid attention recently as a thin film light weight display apparatus to be replaced with cathode ray tubes (CRT) and liquid crystal display (LCD). Studies and developments are vigorously made on an organic EL display apparatus having thin film transistors as switching elements for driving the organic EL display apparatus, among other display apparatuses.
FIG. 6 is a cross sectional view of an organic EL device disclosed in Japanese Patent Laid-open Publication No. 2001-133807. On a transparent substrate 1 whose surface is covered with a silicon oxide film, a top gate type thin film transistor 10 is formed. The thin film transistor (TFT) 10 comprises first and second regions R1 and R2 as a source and a drain, a channel region C between the first and second regions R1 and R2, and a gate electrode G.
An intermediate connection metal 15 is formed on the first region R1 of TFT 10, and a data line 16 is connected to the second region R2. An interlayer insulating film 20 is formed covering TFT 10, intermediate connection metal 15 and data line 16. A transparent pixel electrode 25 made of indium tin oxide (ITO) is formed on the interlayer insulating film 20.
A cover film 26 disposed overlapping the outer periphery of the pixel electrode 25 covers the edge of the pixel electrode 25. An organic light emission layer 30 is formed on the pixel electrode 25 inside the cover film 26. The edge of the organic light emission layer 30 rides on the cover film 26. An upper electrode 35 is formed on the organic light emission layer 30 and interlayer insulating film 20. The cover film 26 prevents a short circuit between the pixel electrode 25 and upper electrode 35.
Photosensitive resist material is used as the material of the cover film 26. By using the photosensitive resist material, the cover film 26 can be patterned by three processes; resist material coating, exposing and development. If other insulating materials are used, additional processes are necessary including etching using a resist pattern and resist pattern removal. As the photosensitive resist is used as the material of the cover film 26, the manufacture processes can be simplified.
It is known that if the surface of an ITO film used as the anode of the organic EL device is forcibly oxidized prior to forming the organic light emission film, the characteristics of the organic EL device can be improved. As the forcible oxidation method, two methods are effective, oxidation using oxygen plasma and ultraviolet radiation in an ozone atmosphere.
If the photosensitive resist is used as the material of the cover film 26 shown in FIG. 6 and the pixel electrode 25 is exposed to oxygen plasma, the cover film 26 is etched. Therefore, ultraviolet radiation in an ozone atmosphere is preferable as the forcible oxidation method for the surface of the pixel electrode 25.
However, as an ultraviolet ray is radiated to the pixel electrode 25, the ultraviolet ray is radiated also to TFT 10. TFT 10 is damaged by the ultraviolet ray and its characteristics are degraded.